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[1.0.X] Fixed #10336 -- Added improved documentation of generic views…

…. Thanks to Jacob and Adrian for the original text (from the DjangoBook), and Ramiro for doing the work of porting the docs.

Merge of r11025 and r11026 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@11027 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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5 docs/internals/documentation.txt
@@ -130,11 +130,6 @@ TODO
The work is mostly done, but here's what's left, in rough order of priority.
- * Fix up generic view docs: adapt Chapter 9 of the Django Book (consider
- this TODO item my permission and license) into
- ``topics/generic-views.txt``; remove the intro material from
- ``ref/generic-views.txt`` and just leave the function reference.
-
* Change the "Added/changed in development version" callouts to proper
Sphinx ``.. versionadded::`` or ``.. versionchanged::`` directives.
View
71 docs/ref/generic-views.txt
@@ -9,67 +9,18 @@ again and again. In Django, the most common of these patterns have been
abstracted into "generic views" that let you quickly provide common views of
an object without actually needing to write any Python code.
-Django's generic views contain the following:
+A general introduction to generic views can be found in the :ref:`topic guide
+<topics-generic-views>`.
- * A set of views for doing list/detail interfaces.
-
- * A set of views for year/month/day archive pages and associated
- detail and "latest" pages (for example, the Django weblog's year_,
- month_, day_, detail_, and latest_ pages).
-
- * A set of views for creating, editing, and deleting objects.
-
-.. _year: http://www.djangoproject.com/weblog/2005/
-.. _month: http://www.djangoproject.com/weblog/2005/jul/
-.. _day: http://www.djangoproject.com/weblog/2005/jul/20/
-.. _detail: http://www.djangoproject.com/weblog/2005/jul/20/autoreload/
-.. _latest: http://www.djangoproject.com/weblog/
-
-All of these views are used by creating configuration dictionaries in
-your URLconf files and passing those dictionaries as the third member of the
-URLconf tuple for a given pattern. For example, here's the URLconf for the
-simple weblog app that drives the blog on djangoproject.com::
-
- from django.conf.urls.defaults import *
- from django_website.apps.blog.models import Entry
-
- info_dict = {
- 'queryset': Entry.objects.all(),
- 'date_field': 'pub_date',
- }
-
- urlpatterns = patterns('django.views.generic.date_based',
- (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/(?P<day>\w{1,2})/(?P<slug>[-\w]+)/$', 'object_detail', info_dict),
- (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/(?P<day>\w{1,2})/$', 'archive_day', info_dict),
- (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/$', 'archive_month', info_dict),
- (r'^(?P<year>\d{4})/$', 'archive_year', info_dict),
- (r'^$', 'archive_index', info_dict),
- )
-
-As you can see, this URLconf defines a few options in ``info_dict``.
-``'queryset'`` gives the generic view a ``QuerySet`` of objects to use (in this
-case, all of the ``Entry`` objects) and tells the generic view which model is
-being used.
-
-Documentation of each generic view follows, along with a list of all keyword
-arguments that a generic view expects. Remember that as in the example above,
-arguments may either come from the URL pattern (as ``month``, ``day``,
-``year``, etc. do above) or from the additional-information dictionary (as for
-``queryset``, ``date_field``, etc.).
+This reference contains details of Django's built-in generic views, along with
+a list of all keyword arguments that a generic view expects. Remember that
+arguments may either come from the URL pattern or from the ``extra_context``
+additional-information dictionary.
Most generic views require the ``queryset`` key, which is a ``QuerySet``
instance; see :ref:`topics-db-queries` for more information about ``QuerySet``
objects.
-Most views also take an optional ``extra_context`` dictionary that you can use
-to pass any auxiliary information you wish to the view. The values in the
-``extra_context`` dictionary can be either functions (or other callables) or
-other objects. Functions are evaluated just before they are passed to the
-template. However, note that QuerySets retrieve and cache their data when they
-are first evaluated, so if you want to pass in a QuerySet via
-``extra_context`` that is always fresh you need to wrap it in a function or
-lambda that returns the QuerySet.
-
"Simple" generic views
======================
@@ -783,12 +734,12 @@ specify the page number in the URL in one of two ways:
/objects/?page=3
- * To loop over all the available page numbers, use the ``page_range``
- variable. You can iterate over the list provided by ``page_range``
+ * To loop over all the available page numbers, use the ``page_range``
+ variable. You can iterate over the list provided by ``page_range``
to create a link to every page of results.
These values and lists are 1-based, not 0-based, so the first page would be
-represented as page ``1``.
+represented as page ``1``.
For more on pagination, read the :ref:`pagination documentation
<topics-pagination>`.
@@ -800,7 +751,7 @@ As a special case, you are also permitted to use ``last`` as a value for
/objects/?page=last
-This allows you to access the final page of results without first having to
+This allows you to access the final page of results without first having to
determine how many pages there are.
Note that ``page`` *must* be either a valid page number or the value ``last``;
@@ -891,7 +842,7 @@ library <topics-forms-index>` to build and display the form.
**Description:**
A page that displays a form for creating an object, redisplaying the form with
-validation errors (if there are any) and saving the object.
+validation errors (if there are any) and saving the object.
**Required arguments:**
View
503 docs/topics/generic-views.txt
@@ -0,0 +1,503 @@
+.. _topics-generic-views:
+
+=============
+Generic views
+=============
+
+Writing Web applications can be monotonous, because we repeat certain patterns
+again and again. Django tries to take away some of that monotony at the model
+and template layers, but Web developers also experience this boredom at the view
+level.
+
+Django's *generic views* were developed to ease that pain. They take certain
+common idioms and patterns found in view development and abstract them so that
+you can quickly write common views of data without having to write too much
+code.
+
+We can recognize certain common tasks, like displaying a list of objects, and
+write code that displays a list of *any* object. Then the model in question can
+be passed as an extra argument to the URLconf.
+
+Django ships with generic views to do the following:
+
+ * Perform common "simple" tasks: redirect to a different page and
+ render a given template.
+
+ * Display list and detail pages for a single object. If we were creating an
+ application to manage conferences then a ``talk_list`` view and a
+ ``registered_user_list`` view would be examples of list views. A single
+ talk page is an example of what we call a "detail" view.
+
+ * Present date-based objects in year/month/day archive pages,
+ associated detail, and "latest" pages. The Django Weblog's
+ (http://www.djangoproject.com/weblog/) year, month, and
+ day archives are built with these, as would be a typical
+ newspaper's archives.
+
+ * Allow users to create, update, and delete objects -- with or
+ without authorization.
+
+Taken together, these views provide easy interfaces to perform the most common
+tasks developers encounter.
+
+Using generic views
+===================
+
+All of these views are used by creating configuration dictionaries in
+your URLconf files and passing those dictionaries as the third member of the
+URLconf tuple for a given pattern.
+
+For example, here's a simple URLconf you could use to present a static "about"
+page::
+
+ from django.conf.urls.defaults import *
+ from django.views.generic.simple import direct_to_template
+
+ urlpatterns = patterns('',
+ ('^about/$', direct_to_template, {
+ 'template': 'about.html'
+ })
+ )
+
+Though this might seem a bit "magical" at first glance -- look, a view with no
+code! --, actually the ``direct_to_template`` view simply grabs information from
+the extra-parameters dictionary and uses that information when rendering the
+view.
+
+Because this generic view -- and all the others -- is a regular view functions
+like any other, we can reuse it inside our own views. As an example, let's
+extend our "about" example to map URLs of the form ``/about/<whatever>/`` to
+statically rendered ``about/<whatever>.html``. We'll do this by first modifying
+the URLconf to point to a view function:
+
+.. parsed-literal::
+
+ from django.conf.urls.defaults import *
+ from django.views.generic.simple import direct_to_template
+ **from mysite.books.views import about_pages**
+
+ urlpatterns = patterns('',
+ ('^about/$', direct_to_template, {
+ 'template': 'about.html'
+ }),
+ **('^about/(\w+)/$', about_pages),**
+ )
+
+Next, we'll write the ``about_pages`` view::
+
+ from django.http import Http404
+ from django.template import TemplateDoesNotExist
+ from django.views.generic.simple import direct_to_template
+
+ def about_pages(request, page):
+ try:
+ return direct_to_template(request, template="about/%s.html" % page)
+ except TemplateDoesNotExist:
+ raise Http404()
+
+Here we're treating ``direct_to_template`` like any other function. Since it
+returns an ``HttpResponse``, we can simply return it as-is. The only slightly
+tricky business here is dealing with missing templates. We don't want a
+nonexistent template to cause a server error, so we catch
+``TemplateDoesNotExist`` exceptions and return 404 errors instead.
+
+.. admonition:: Is there a security vulnerability here?
+
+ Sharp-eyed readers may have noticed a possible security hole: we're
+ constructing the template name using interpolated content from the browser
+ (``template="about/%s.html" % page``). At first glance, this looks like a
+ classic *directory traversal* vulnerability. But is it really?
+
+ Not exactly. Yes, a maliciously crafted value of ``page`` could cause
+ directory traversal, but although ``page`` *is* taken from the request URL,
+ not every value will be accepted. The key is in the URLconf: we're using
+ the regular expression ``\w+`` to match the ``page`` part of the URL, and
+ ``\w`` only accepts letters and numbers. Thus, any malicious characters
+ (dots and slashes, here) will be rejected by the URL resolver before they
+ reach the view itself.
+
+Generic views of objects
+========================
+
+The ``direct_to_template`` certainly is useful, but Django's generic views
+really shine when it comes to presenting views on your database content. Because
+it's such a common task, Django comes with a handful of built-in generic views
+that make generating list and detail views of objects incredibly easy.
+
+Let's take a look at one of these generic views: the "object list" view. We'll
+be using these models::
+
+ # models.py
+ from django.db import models
+
+ class Publisher(models.Model):
+ name = models.CharField(max_length=30)
+ address = models.CharField(max_length=50)
+ city = models.CharField(max_length=60)
+ state_province = models.CharField(max_length=30)
+ country = models.CharField(max_length=50)
+ website = models.URLField()
+
+ def __unicode__(self):
+ return self.name
+
+ class Meta:
+ ordering = ["-name"]
+
+ class Book(models.Model):
+ title = models.CharField(max_length=100)
+ authors = models.ManyToManyField('Author')
+ publisher = models.ForeignKey(Publisher)
+ publication_date = models.DateField()
+
+To build a list page of all books, we'd use a URLconf along these lines::
+
+ from django.conf.urls.defaults import *
+ from django.views.generic import list_detail
+ from mysite.books.models import Publisher
+
+ publisher_info = {
+ "queryset" : Publisher.objects.all(),
+ }
+
+ urlpatterns = patterns('',
+ (r'^publishers/$', list_detail.object_list, publisher_info)
+ )
+
+That's all the Python code we need to write. We still need to write a template,
+however. We could explicitly tell the ``object_list`` view which template to use
+by including a ``template_name`` key in the extra arguments dictionary, but in
+the absence of an explicit template Django will infer one from the object's
+name. In this case, the inferred template will be
+``"books/publisher_list.html"`` -- the "books" part comes from the name of the
+app that defines the model, while the "publisher" bit is just the lowercased
+version of the model's name.
+
+.. highlightlang:: html+django
+
+This template will be rendered against a context containing a variable called
+``object_list`` that contains all the book objects. A very simple template
+might look like the following::
+
+ {% extends "base.html" %}
+
+ {% block content %}
+ <h2>Publishers</h2>
+ <ul>
+ {% for publisher in object_list %}
+ <li>{{ publisher.name }}</li>
+ {% endfor %}
+ </ul>
+ {% endblock %}
+
+That's really all there is to it. All the cool features of generic views come
+from changing the "info" dictionary passed to the generic view. The
+:ref:`generic views reference<ref-generic-views>` documents all the generic
+views and all their options in detail; the rest of this document will consider
+some of the common ways you might customize and extend generic views.
+
+Extending generic views
+=======================
+
+.. highlightlang:: python
+
+There's no question that using generic views can speed up development
+substantially. In most projects, however, there comes a moment when the
+generic views no longer suffice. Indeed, the most common question asked by new
+Django developers is how to make generic views handle a wider array of
+situations.
+
+Luckily, in nearly every one of these cases, there are ways to simply extend
+generic views to handle a larger array of use cases. These situations usually
+fall into a handful of patterns dealt with in the sections that follow.
+
+Making "friendly" template contexts
+-----------------------------------
+
+You might have noticed that our sample publisher list template stores all the
+books in a variable named ``object_list``. While this works just fine, it isn't
+all that "friendly" to template authors: they have to "just know" that they're
+dealing with books here. A better name for that variable would be
+``publisher_list``; that variable's content is pretty obvious.
+
+We can change the name of that variable easily with the ``template_object_name``
+argument:
+
+.. parsed-literal::
+
+ publisher_info = {
+ "queryset" : Publisher.objects.all(),
+ **"template_object_name" : "publisher",**
+ }
+
+ urlpatterns = patterns('',
+ (r'^publishers/$', list_detail.object_list, publisher_info)
+ )
+
+Providing a useful ``template_object_name`` is always a good idea. Your
+coworkers who design templates will thank you.
+
+Adding extra context
+--------------------
+
+Often you simply need to present some extra information beyond that provided by
+the generic view. For example, think of showing a list of all the other
+publishers on each publisher detail page. The ``object_detail`` generic view
+provides the publisher to the context, but it seems there's no way to get a list
+of *all* publishers in that template.
+
+But there is: all generic views take an extra optional parameter,
+``extra_context``. This is a dictionary of extra objects that will be added to
+the template's context. So, to provide the list of all publishers on the detail
+detail view, we'd use an info dict like this:
+
+.. parsed-literal::
+
+ from mysite.books.models import Publisher, **Book**
+
+ publisher_info = {
+ "queryset" : Publisher.objects.all(),
+ "template_object_name" : "publisher",
+ **"extra_context" : {"book_list" : Book.objects.all()}**
+ }
+
+This would populate a ``{{ book_list }}`` variable in the template context.
+This pattern can be used to pass any information down into the template for the
+generic view. It's very handy.
+
+However, there's actually a subtle bug here -- can you spot it?
+
+The problem has to do with when the queries in ``extra_context`` are evaluated.
+Because this example puts ``Publisher.objects.all()`` in the URLconf, it will
+be evaluated only once (when the URLconf is first loaded). Once you add or
+remove publishers, you'll notice that the generic view doesn't reflect those
+changes until you reload the Web server (see :ref:`caching-and-querysets`
+for more information about when QuerySets are cached and evaluated).
+
+.. note::
+
+ This problem doesn't apply to the ``queryset`` generic view argument. Since
+ Django knows that particular QuerySet should *never* be cached, the generic
+ view takes care of clearing the cache when each view is rendered.
+
+The solution is to use a callback in ``extra_context`` instead of a value. Any
+callable (i.e., a function) that's passed to ``extra_context`` will be evaluated
+when the view is rendered (instead of only once). You could do this with an
+explicitly defined function:
+
+.. parsed-literal::
+
+ def get_books():
+ return Book.objects.all()
+
+ publisher_info = {
+ "queryset" : Publisher.objects.all(),
+ "template_object_name" : "publisher",
+ "extra_context" : **{"book_list" : get_books}**
+ }
+
+or you could use a less obvious but shorter version that relies on the fact that
+``Publisher.objects.all`` is itself a callable:
+
+.. parsed-literal::
+
+ publisher_info = {
+ "queryset" : Publisher.objects.all(),
+ "template_object_name" : "publisher",
+ "extra_context" : **{"book_list" : Book.objects.all}**
+ }
+
+Notice the lack of parentheses after ``Book.objects.all``; this references
+the function without actually calling it (which the generic view will do later).
+
+Viewing subsets of objects
+--------------------------
+
+Now let's take a closer look at this ``queryset`` key we've been using all
+along. Most generic views take one of these ``queryset`` arguments -- it's how
+the view knows which set of objects to display (see :ref:`topics-db-queries` for
+more information about ``QuerySet`` objects, and see the
+:ref:`generic views reference<ref-generic-views>` for the complete details).
+
+To pick a simple example, we might want to order a list of books by
+publication date, with the most recent first:
+
+.. parsed-literal::
+
+ book_info = {
+ "queryset" : Book.objects.all().order_by("-publication_date"),
+ }
+
+ urlpatterns = patterns('',
+ (r'^publishers/$', list_detail.object_list, publisher_info),
+ **(r'^books/$', list_detail.object_list, book_info),**
+ )
+
+
+That's a pretty simple example, but it illustrates the idea nicely. Of course,
+you'll usually want to do more than just reorder objects. If you want to
+present a list of books by a particular publisher, you can use the same
+technique:
+
+.. parsed-literal::
+
+ **acme_books = {**
+ **"queryset": Book.objects.filter(publisher__name="Acme Publishing"),**
+ **"template_name" : "books/acme_list.html"**
+ **}**
+
+ urlpatterns = patterns('',
+ (r'^publishers/$', list_detail.object_list, publisher_info),
+ **(r'^books/acme/$', list_detail.object_list, acme_books),**
+ )
+
+Notice that along with a filtered ``queryset``, we're also using a custom
+template name. If we didn't, the generic view would use the same template as the
+"vanilla" object list, which might not be what we want.
+
+Also notice that this isn't a very elegant way of doing publisher-specific
+books. If we want to add another publisher page, we'd need another handful of
+lines in the URLconf, and more than a few publishers would get unreasonable.
+We'll deal with this problem in the next section.
+
+.. note::
+
+ If you get a 404 when requesting ``/books/acme/``, check to ensure you
+ actually have a Publisher with the name 'ACME Publishing'. Generic
+ views have an ``allow_empty`` parameter for this case. See the
+ :ref:`generic views reference<ref-generic-views>` for more details.
+
+Complex filtering with wrapper functions
+----------------------------------------
+
+Another common need is to filter down the objects given in a list page by some
+key in the URL. Earlier we hard-coded the publisher's name in the URLconf, but
+what if we wanted to write a view that displayed all the books by some arbitrary
+publisher? We can "wrap" the ``object_list`` generic view to avoid writing a lot
+of code by hand. As usual, we'll start by writing a URLconf:
+
+.. parsed-literal::
+
+ from mysite.books.views import books_by_publisher
+
+ urlpatterns = patterns('',
+ (r'^publishers/$', list_detail.object_list, publisher_info),
+ **(r'^books/(\w+)/$', books_by_publisher),**
+ )
+
+Next, we'll write the ``books_by_publisher`` view itself::
+
+ from django.http import Http404
+ from django.views.generic import list_detail
+ from mysite.books.models import Book, Publisher
+
+ def books_by_publisher(request, name):
+
+ # Look up the publisher (and raise a 404 if it can't be found).
+ try:
+ publisher = Publisher.objects.get(name__iexact=name)
+ except Publisher.DoesNotExist:
+ raise Http404
+
+ # Use the object_list view for the heavy lifting.
+ return list_detail.object_list(
+ request,
+ queryset = Book.objects.filter(publisher=publisher),
+ template_name = "books/books_by_publisher.html",
+ template_object_name = "books",
+ extra_context = {"publisher" : publisher}
+ )
+
+This works because there's really nothing special about generic views -- they're
+just Python functions. Like any view function, generic views expect a certain
+set of arguments and return ``HttpResponse`` objects. Thus, it's incredibly easy
+to wrap a small function around a generic view that does additional work before
+(or after; see the next section) handing things off to the generic view.
+
+.. note::
+
+ Notice that in the preceding example we passed the current publisher being
+ displayed in the ``extra_context``. This is usually a good idea in wrappers
+ of this nature; it lets the template know which "parent" object is currently
+ being browsed.
+
+Performing extra work
+---------------------
+
+The last common pattern we'll look at involves doing some extra work before
+or after calling the generic view.
+
+Imagine we had a ``last_accessed`` field on our ``Author`` object that we were
+using to keep track of the last time anybody looked at that author::
+
+ # models.py
+
+ class Author(models.Model):
+ salutation = models.CharField(max_length=10)
+ first_name = models.CharField(max_length=30)
+ last_name = models.CharField(max_length=40)
+ email = models.EmailField()
+ headshot = models.ImageField(upload_to='/tmp')
+ last_accessed = models.DateTimeField()
+
+The generic ``object_detail`` view, of course, wouldn't know anything about this
+field, but once again we could easily write a custom view to keep that field
+updated.
+
+First, we'd need to add an author detail bit in the URLconf to point to a
+custom view:
+
+.. parsed-literal::
+
+ from mysite.books.views import author_detail
+
+ urlpatterns = patterns('',
+ #...
+ **(r'^authors/(?P<author_id>\d+)/$', author_detail),**
+ )
+
+Then we'd write our wrapper function::
+
+ import datetime
+ from mysite.books.models import Author
+ from django.views.generic import list_detail
+ from django.shortcuts import get_object_or_404
+
+ def author_detail(request, author_id):
+ # Look up the Author (and raise a 404 if she's not found)
+ author = get_object_or_404(Author, pk=author_id)
+
+ # Record the last accessed date
+ author.last_accessed = datetime.datetime.now()
+ author.save()
+
+ # Show the detail page
+ return list_detail.object_detail(
+ request,
+ queryset = Author.objects.all(),
+ object_id = author_id,
+ )
+
+.. note::
+
+ This code won't actually work unless you create a
+ ``books/author_detail.html`` template.
+
+We can use a similar idiom to alter the response returned by the generic view.
+If we wanted to provide a downloadable plain-text version of the list of
+authors, we could use a view like this::
+
+ def author_list_plaintext(request):
+ response = list_detail.object_list(
+ request,
+ queryset = Author.objects.all(),
+ mimetype = "text/plain",
+ template_name = "books/author_list.txt"
+ )
+ response["Content-Disposition"] = "attachment; filename=authors.txt"
+ return response
+
+This works because the generic views return simple ``HttpResponse`` objects
+that can be treated like dictionaries to set HTTP headers. This
+``Content-Disposition`` business, by the way, instructs the browser to
+download and save the page instead of displaying it in the browser.
View
1  docs/topics/index.txt
@@ -14,6 +14,7 @@ Introductions to all the key parts of Django you'll need to know:
forms/index
forms/modelforms
templates
+ generic-views
files
testing
auth
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